The objective of this research project is to determine the factors which are responsible for the regulation of blood flow to a solid tumor. The V-2 carcinoma will be used in New Zealand white rabbits 14 days after implantation. Blood flow will be measured in the awake unanesthetized rabbits using the microsphere technique. Chronic catheters will have been implanted 3 days before the measurememt of blood flows. This technique permits the blood flow to the tumor and other organs to be measured. Microspheres with four separable isotopes will be used to measure blood flows in the control condition, and at 5, 10 and 15 minutes after the injection of the appropriate drug. Dose response curves and the time course of the responses will be constructed. The emphasis will be on the role of the prostaglandins in the regulation of tumor blood flow. The effect of prostaglandin synthetase inhibitors on the response of tumor blood flows to exogenous prostaglandins will also be examined.